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High-mass Dimuon Resonances in Pb-Pb Collisions at 5.5 TeV in CMS

High-mass Dimuon Resonances in Pb-Pb Collisions at 5.5 TeV in CMS. Dipanwita Dutta BARC, India On behalf of the CMS Collaboration. Outline. Physics Motivation: Dimuons from Quarkonia and Z 0 CMS Experimental Setup Simulation for Dimuons Results Summary. . LHC. RHIC.

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High-mass Dimuon Resonances in Pb-Pb Collisions at 5.5 TeV in CMS

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  1. High-mass Dimuon Resonances in Pb-Pb Collisions at 5.5 TeV in CMS Dipanwita Dutta BARC, India On behalf of the CMS Collaboration QM’08, Jaipur

  2. Outline • Physics Motivation: • Dimuons from Quarkonia and Z0 • CMS Experimental Setup • Simulation for Dimuons • Results • Summary QM’08, Jaipur

  3. LHC RHIC Vogt, hep-ph/0205330 Dimuons: From SPS, RHIC to LHC • LHC: Factor 30-45 increase in energy compared to RHIC • Heavy Ion Physics at LHC • Plasma Hotter, Bigger and Longer life time • Access to lower x and higher Q2 • Unprecedented gluon Density • Availability of new Probes (Y,Y',Y") • Z0with large cross-section 20 High Mass Dimuon Resonances at LHC J/, Y,Y',Y", Z0 QM’08, Jaipur

  4. Suppression: RHIC comparable to SPS • Regeneration compensate screening • J/ not screened at RHIC (TD~2Tc)? • Suppression via feed down • LHC: recombination or suppression •  Large Cross-section: 20×RHIC •  melts only at LHC: TD~4 TC • Small bb(bar) pairs: less regeneration • Much cleaner probe than J/ • LHC: Y will slove the puzzle of suppression Suppression of C’onium States Suppression of B’onium States y’ cc Dimuons :Probe of Dense QCD Medium Dissociation of Q’nia (Debye Screening): Hot QCD Thermometer • Z0 : Weak production and decay-- No final state effect • Baseline for Quarkonium Suppression QM’08, Jaipur

  5. Z0 Production via qq annihilation Z0 Production via qq annihilation 10-6 10-4 10-2 100 Z0 x M2 (GeV2) QQ Production via gluon fusion  J/ Gluon saturation: CGC Dimuons: Probe of Initial State state in a novel Bjorken-x range (10-3-10-5): • nuclear shadowing, • high-density saturated gluon distribution. 108 106 104 102 100 QM’08, Jaipur

  6. CMS Detector for Heavy Ions Muon system: Drift Tubes (DT) in central barrel region Cathode Strip Chambers (CSC) in endcap region Resistive Plate Chambers (RPC) in barrel and endcap } precise measurement of position (momentum) fast info for LVL-1 trigger Excellent coverage: ~5 units of rapidity and 2 Strongest magnetic field: 4 T, 2 T (return yoke) Tag from muon stations, momentum resolution from Silicon tracker: ~2% of momentum resolution for tracks with pT <100 GeV Ecal+Hcal+Coil – absorbs hadrons Coil HCAL Tracker ECAL QM’08, Jaipur

  7. Dimuon Sources at LHC : Signal and Background • Signal Dimuon Resonances: • Quarkonia: J/ (BR: 5.9%),  (BR: 2.5%) • Z0: (BR: 3.4%) • Background Dimuons: • Decays from open c and b • Decays from , K • Decays from W • Mixed muon pairs QM’08, Jaipur

  8. Simulation of Quarkonia Marc Bedjidian, Olga Kodolova,CMS NOTE-2006/089 Resonance cross-section (b): • Signal (J/,):CEM, NLO-pp, (CTEQ5M+EKS98 PDF),TAA scaled • Background Uncorrelated Muon Pairs from /K decays: • Two scenarios for the multiplicity of charged particles • dNch/d = 2500 at =0 • dNch/d = 5000 at =0 • – Only  and Kare considered( 90% of charged particles multiplicity) • – Kaon/pion = 11% (HIJING) –pT and  distributions of pions and kaons according to HIJING • Background Muons from Open Heavy Quark (b,c): • NLO pp, CTEQ5M+EKS98 PDF, TAA scaled b=0 5% c.c. min.bias. N(cc) w/o shadowing 226 206 51 w/ shadowing 150 135 33 b=0 5% c.c. min.bias. N(bb) w/o shadowing 6 5.5 1.4 w/ shadowing 5 4.7 1.2 QM’08, Jaipur

  9. Z = 190m Dimuon reconstruction algorithm for Quarkonia QM’08, Jaipur

  10. Dimuon High Level Trigger performance for Heavy Ions Two Different Level 1 Trigger: (single muon trigger) L1: optimised for High luminosity pp run OL1: low quality muon candidates optimised for HI L2 and L3 run on online farm: Trigger Conditions: Two L1 or L2 opposite sign+ L3 (cut on loose) J/y trigger efficiency: 0.97% (OL1-L2 chain) 0.44% (L1-L2 chain) trigger efficiency: 21% (OL1-L2 chain) 16.5% (L1-L2 chain) QM’08, Jaipur

  11. Dimuon efficiency & purity vs dNch/dy Y is embedded in PbPb events Efficiency: Eff = Efftrk-1 x Efftrk-2 x Effvtx > 80% for all multiplicity (barrel) > 65% for all multiplicity (barrel+endcap) Purity = [true Y reco]/[all vtx reco] > 90% (all multiplicities) “realistic” LHC multiplicity range QM’08, Jaipur

  12. “high” multiplicity dNch/dη|η=0 = 5000 “low” multiplicity dNch/dh|h=0 = 2500 J/y mass spectra (like-sign subtraction) sJ/y= 35 MeV/c2 in (barrel+endcap), Both muons with ||<2.4 S/B=1.2 S/B=0.6 QM’08, Jaipur

  13.  mass spectra (like-sign subtraction) “high” multiplicity dNch/dh|η=0 = 5000 Excellent Mass Resolution at LHC: sY = 54 MeV/c2 in (barrel) and  =90 MeV/c2 in (barrel+endcap) S/B=0.97 Barrel: Both muons with |h|<0.8 Barrel+ endcap: Both muons with |h|<2.4 S/B=0.12 QM’08, Jaipur

  14. pT and  reach of Quarkonia (1 Pb-Pb run) For 1 month LHC run, L int =0.5 nb-1  ofJ/  of  Very Large Statistics N(J/)~105 N()~104 pT of  pT ofJ/ pT reach ~40 GeV (without suppression) QM’08, Jaipur

  15. Simulation for Z0+- : Gen. level D. Dutta et. al Expected No. for one month LHC run, Lint=0.5 nb-1 BR in Z0+- ~ 3.4% CMS Muon Acceptance : pT () > 3.5 GeV, |()|<2.4 Acceptance of Z0~55% qq(bar)Z0(Z0+jet) Total Dominant Contribution for Z0 prod: qq(bar) annihilationStudy of Quark PDF Shadowing qg(Z0+jet) QM’08, Jaipur

  16. Simulation for Z0 +- +DY Dimuons: bb(bar) fragmentation ~ dominant contribution Combinatorial background: b and ,K ~16% ,K and charm decay: 5-6% Signal from Z0: Clear peak ~11,000 events in MZ±10 GeV/c2, Less than 5% background CMS Physics TDR: Addendum to High Density QCD with Heavy Ions, J. Phys. G, Nucl. Part. Phys. 34 (2007) 2304 QM’08, Jaipur

  17. *- ,Z- jet tagging ‏ D. Dutta, C.Mironov et al. • CMS can also calibrate jet-energy loss with back-to-back Z and/or virtual  (large cross-sections, good detection capabilities): • Dominant (heavy-Q) dimuon backgd. • “removable” via secondary-vtx. cut Dimuon trigger NZ-jet~103 Z0/g* q/g Away side Associated Hadrons pT >25 GeV/c sr=50 mm sj=20 mm 3s vtx. cut QM’08, Jaipur

  18. Summary • J/, and Z0:Prominent probe of QCD media in Pb+Pb collisions • Stepwise melting– Thermometer of QGP • Quarkonia production via gg fusion: • probe of low x QCD • Z0 production via qqbar annihilation: • Probe of Nuclear shadowing of quark PDF • Simulation Studiesof J/,: • Acceptance :J/~15%(at high pT) and ~26% • Dimuon Efficiency ~80% and purity 90% • Mass Resolutions at LHC: σ=~1% MQQ(barrel+endcap),σJ/=35 MeV/c2(barrel+endcap) σ=54 MeV/c2(barrel alone) • Signal/Background: ~5(1), ~1(0.1) for J/, in barrel (+endcaps) • High rate expected (per year): J/ ~ 180 kevents, Y ~ 25 kevents, Y’ ~ 7 kevents, Y’’ ~ 4 kevents • High pT reach~ 40 GeV • Generator Studies of Z0: Aceeptance: Z0~55% No. of Z0: ~103(104) for 10% central (Minbias) within CMS acceptance Thank you QM’08, Jaipur

  19. Back Up Slides QM’08, Jaipur

  20. Quarkonia production: kinematical spectra pT and h according to Yellow Report, CERN-2004-009, hep-ph/0311048 J/y Y J/y Y QM’08, Jaipur

  21. Heavy quark pairs production: kinematical spectra pT and h according to Yellow Report, CERN-2004-009, hep-ph/0311048 bbbar ccbar QM’08, Jaipur

  22. J/y and Y trigger strategy L1 Trigger: single muon trigger with no momentum cuts optimized for HI run conditions L2 and L3: run on online farm L2 trigger condition: either opposite(like) sign dimuon candidate at L1 trigger or opposite(like) sign dimuon candidate at L2 trigger L3 includes regional track finder starting from the muon stations, primary vertex finder with pixel detectors and dimuon vertex constraints QM’08, Jaipur

  23. Dissociation (Color Screening): Hot QCD Thermometer QM’08, Jaipur

  24. Quarkonia rates and S/B ratio at CMS Signal-to-background ratio and expected quarkonia yields in one month of PbPb running (0.5 nb-1 integrated luminosity) for two multiplicity scenarios and two h windows No of J/ ~105 and No. of  ~ 104in Minbias Event QM’08, Jaipur

  25. Dimuon Sources at LHC : Signal and Background • Signal Dimuon Resonances: • Quarkonia: J/ (BR: 5.9%),  (BR: 2.5%) • Z0: (BR: 3.4%) • Background Dimuons: • Decays from open c and b • Decays from , K • Decays from W • Mixed muon pairs QM’08, Jaipur

  26. Cross-sections for Z0 QM’08, Jaipur

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